In general, in a conventional rotary connector, a flexible flat cable shares high percentage of the total cost of the rotary connector. A proposal disclosed in the Japanese Non-Examined Patent Publication H4-310445 is an example for saving the cost by decreasing the length of the flexible flat cable.
Hereinafter the conventional rotary connector is described referring to FIG. 14 through FIG. 16.
FIG. 14 is a cross sectional plan view showing the conventional rotary connector, FIG. 15 is a cross sectional side view showing the main portion of the same, and FIG. 16 is an exploded view showing the conventional rotary connector.
As shown in the illustrations, at the inner side of an annular outer case 510, an inner case 520 is disposed in such a manner as to be rotatable relatively to the outer case 510. The inner case 520 comprises a cylindrical portion 522 and a cover portion 521 which covers the upper side of an annular space 540 formed with the inner wall 511 of the annular outer case 510 and the outer wall of the cylindrical portion 522 of the inner case 520. A lower-side-cover 530 is fixed to the lower side of the annular outer case 510, and covers the lower side of the annular space 540.
In the annular space 540, a flexible flat cable 550 is disposed. The respective ends (551,552) of the cable 550 are respectively fixed to the outer case 510 and to the inner case 520, by which the outer case 510 and the inner case 520 are electrically connected as well. The outer case 510 and the inner case 520 are respectively further electrically connected to outer electrical circuits. In the annular space 540, the cable 550 is wound along the inner wall 511 of the outer case 510 in a first direction, and along the outer wall of the cylindrical portion 552 of the inner case 520 in a second direction which is opposite to the first direction via a U-shaped reversed-portion 553.
In the annular space 540, a plurality of rollers 570, which are connected by a connecting member 560 along the annular space 540, are disposed. The rollers 570 respectively rotate, and, guide and regulate the cable 550 wound along the annular space 540. Rollers 571 and 572 disposed at the respective end portions (i.e. cut-portion 561) of the connecting member 560 guide the cable 550 which passes through the cut-portion 561 to be reversed along the rollers 571 and 572.
In the above structure, when the inner case 520 is counterclockwise rotated, the cable 550 is wound off from the side of the cylindrical portion 522 of the inner case 520, and the reversed-portion 553 of the cable 550 presses the roller 571, whereby the connecting member 560 is counterclockwise rotated and the cable 550 becomes the state of wound-off (i.e., the dimension of the cable 550 becomes longer than before at the side of the inner wall 511 of the outer case 510).
On the other hand, when the inner case 520 is clockwise rotated, the cable 550 is wound up toward the side of the cylindrical portion 522 of the inner case 520 and presses the roller 572, whereby the connecting member 560 is rotated clockwise and the cable 550 becomes the state of wound-up (i.e., the dimension of the cable 550 becomes longer than before at the side of the cylindrical portion 522 of the inner case 520).
However, in the above conventional structure, predetermined clearances are formed between the rollers (570,571,572) and the outer case 510, and, between the rollers and the inner case 520, also between the connecting member 560 and the outer case 510, also between the connecting member 560 and the inner case 520, for enabling the winding of the cable 550 and for enabling the rotation of the rollers. Also the mass of the rollers are large. Therefore, when a vibration is applied to the rotary connector during driving a motor vehicle for instance, an audible noise caused by the each-other's bumps of the component parts of the rotary connector occurs.
Also, when the inner case 520 is rotated, the connecting member 560 is moved along the rotating direction of the inner case 520 in the annular space 540. In this case, the reversed-portion 553 of the cable 550 presses the roller (571,572), which causes the damage of the cable 550 due to the stress applied to the flat cable 550.